1. Field of the Invention
The present invention relates to a rotary tool that is capable of firmly fastening bolts or other devices by exerting an impact force on an anvil, to which the tool or another device is attached, in a rotational direction.
2. Description of the Related Art
To date, a rotary tool is known that is capable of firmly fastening bolts or other devices by exerting an impact force on an anvil, to which the tool or another device is attached, in a rotational direction. For example, Japanese Unexamined Patent Application Publication No. 2010-280021 discloses, in FIG. 1, a rotary tool that includes a spindle rotated by a motor, a main hammer disposed at one end portion of the spindle in an axial direction, a secondary hammer disposed so as to cover the outer circumference of the main hammer, and an anvil disposed on the outer side of the main hammer in the axial direction. In the configuration disclosed in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2010-280021, the main hammer is rotatable together with the spindle and movable relative to the spindle in the axial direction. The main hammer includes first pawls and the anvil includes second pawls engageable with the first pawls.
In the above-described configuration, when a torque exceeding a predetermined value is transmitted from the spindle to the main hammer, an impact force is exerted on the anvil in the rotational direction by moving the main hammer toward the anvil while rotating the main hammer to cause the first pawls of the main hammer to become engaged with the second pawls of the anvil with an impact.
Here, in the configuration disclosed in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2010-280021, the secondary hammer is connected to the main hammer with needle rollers interposed therebetween so as to rotate together with the main hammer and allow the main hammer to move in the axial direction. Here, the needle rollers are rotatably disposed in semicircular grooves formed in the main hammer and the secondary hammer.
In such a rotary tool having the above-described configuration, the rotation axis of the secondary hammer has to coincide with the rotation axis of the spindle for vibration reduction. Thus, as illustrated in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2010-280021, a configuration is known in which the rotation axis of the secondary hammer and the rotation axis of the spindle are made coincide with each other as a result of moving an inner circumferential portion of the cylindrical secondary hammer so as to slide over the outer circumferential surface of the spindle.
However, in the configuration such as the one described above in which the inner circumferential portion of the secondary hammer is moved to slide over the outer circumferential surface of the spindle, the sliding portion wears away. This wearing away may adversely affect the performance or the life of the tool.
A configuration made to address this problem is known as illustrated in, for example, FIG. 5 of Japanese Unexamined Patent Application Publication No. 2010-280021, in which the rotation axis of the secondary hammer is made coincide with the rotation axis of the spindle by supporting the cylindrical secondary hammer with a bearing. Specifically, in the configuration disclosed in FIG. 5 of Japanese Unexamined Patent Application Publication No. 2010-280021, the rotation axis of the secondary hammer and the rotation axis of the spindle are made coincide with each other by causing the inner circumference of the casing to support the outer circumferential surface of the cylindrical secondary hammer using a bearing.
In the configuration in which the inner circumference of the casing is caused to support the outer circumferential surface of the cylindrical secondary hammer using a bearing, as in the configuration illustrated in FIG. 5 of Japanese Unexamined Patent Application Publication No. 2010-280021, the number of components increases due to the need of a bearing and the size of the rotary tool increases with increasing length of the rotary tool in the axial direction of the spindle.
On the other hand, a configuration for forming a compact rotary tool is conceivable by reducing the size of the main hammer and the secondary hammer. Reducing the size of the main hammer and the secondary hammer in this manner, however, would reduce the impact torque applied to the anvil, thereby reducing the fastening torque of the rotary tool.